Conventional roof deck design typically calls for wood blocking at the termination points of the roof deck assembly and at the transitions between multiple roof decks, such as expansion joints. The wood blocking is used to provide starting and stopping points for the roof decking, roof insulation, and the roof covering, as well as an anchorage medium for sheet metal flashing and gutter hardware. The wood members can be made a part of the assembly, or can act as fillers, independent from the roof deck assembly, being mounted to a wall or other non-roof deck component. Roof deck stress occurs at the joints between the wood blocking and roof assembly and at the termination points of the roof deck.
As relatively thin, plate-like structures, roofs experience diaphragm forces due to building movement induced by wind and seismic loading. These diaphragm forces result in stress between roof components, especially at roof transition and termination points. These stresses are transferred to the wood blocking and roof supporting structure. Further stress is caused by linear expansion and contraction forces. Since the roof components are formed of different materials with different coefficients of thermal expansion, they can undergo significant relative thermal growth. Such relative movement results in local stresses between the roofing and blocking materials and between the roof assembly and the roof support system. These stresses also occur at the junctures between multiple roof assemblies.
Further problems arise with wood blocking as the wood ages. As it dries, the wood shrinks, warps and buckles, losing its dimensional stability and its ability to retain fasteners. This presents problems for building flashing as it causes substrate movement and fastener loosening resulting in leaks and failures.
To deal with these problems, there is need for improved protection from the stresses between the roof deck and the roof supporting structure at the roof deck perimeter and between adjoining roof assemblies.